The V8 Owners Forum -

I've a pair of heads that've been ported and fitted with slightly larger valves (41mm inlet/35mm exhaust), they were also heavily skimmed to remove damage caused by something hard the engine ingested.
I seem to have ended up with a very high compression ratio, still pinking on Tesco 99 octane and Shell V power even with composite gaskets and the ignition retarded to 21° maximum advance so I need to reduce the compression if I want to use these heads.
I was wondering if I could draw a circle around each valve that almost extends to the bore diameter (or the head gasket if that's smaller) and remove metal from the 'corners', ie about 6 to 9 o/clock on the exhaust and 3 to 6 on the inlet valve when viewed with the spark plug above the valves?
I think there was a small bump by the spark plug, can this be removed?
I don't want to change the pistons, is there anything else I could do?

Maybe easier to get thicker head gaskets?, can gaskets be custom made?

Chris.

If you're using 14 bolt heads on a 94mm bore I can supply 0.098" MLS gaskets.

They're not cheap though at around £230

I have removed several CC's worth of metal out of a set of heads using a burr, I removed it from the area opposite the spark plug, in effect the squish band area, the squish does not work on a Rover head due to the dished pistons so it makes no odds removing the metal. It takes ages to do this work and you need a burette and piece of perspex to check how much you have opened the chambers up. I reckon it can take 30-40 minutes per chamber!

Sounds like you have a really high CR and I doubt that you can remove enough material from the chamber to really have a big impact on CR.

Thanks for the replies, I'll have to measure the chamber volume and see if I can remove enough metal - they were originally 28cc, does anyone know what the minimum volume is that I could get away with for a road engine?

Rossco, do you know how much volume the MLS gaskets add compared to composite gaskets like Elrings please?

Conservatively 10cc to 11cc

Cheers, I'll be stripping the engine towards winter and checking the volumes then.
As you say, the gaskets aren't cheap but if it looks like I won't be able to remove enough metal then they may save me from scrapping the heads.

What actually is your CR ?

stevieturbo wrote:What actually is your CR ?

Always a good starting point

Unfortunately I don't know what it is, with hindsight I suppose I should have checked before I put it all back together especially since the heads were skimmed and I didn't ask by how much
I won't be able to get around to taking this engine apart until winter (too many other jobs to do) so I'm just exploring options hoping I can avoid scrapping the heads.
I think maybe my best option is to make a male mould, use it to make a plasticine chamber which I can re-shape to see how much volume I can add and go from there?

Personally I would not use clay or anything like that when trying to work out the chamber volume, just use water and a plate of Perspex, you also need a burette, you can get plastic ones off ebay fro a few quid, I have a glass one and I can tell you that you only have to look at them in a funny way and they break!

You can also burette the pistons at TDC, use some grease around the top of the bore to seal the piston. Finally once you know the head gasket thickness its just some maths the work out the CR.

Is there enough meat on the cylinder head to take off far too much with a composite gasket?

My 36cc heads have had about 1.2mm removed without any issues.

BTW all the 36cc heads that I have buretted have never actually been 36cc, they are more like 32cc

Are you sure spark timing is correct ?

Are you sure valve timing is correct ?

What sort of compression are you seeing on a compression test ?